There is trick that was used by many existing FDB users: do not shoot for the best bare performance (e.g. transaction latency) from the start. Instead 1) benchmark your setup a) bare fdb cluster b) and, application using fdb cluster, 2) secure monitoring (e.g. AFAIU available disk space is very top priority) 3) configure the backup system 4) and plan and script a recovery plan.
Make it work, make it right, then make it fast
FDB provides an awesome potential for growth both from a number of user perspective, AND from a product feature perspective, there is a clear way to scale-up, but to scale-up you need to deliver, and FDB is also great to deliver complex features even without SQL layer. Getting a good grasp on the public interface whatever the programming language is very economical.